From the email that was sent:
Your purchase entitles you to a FREE 1-year data subscription with MyHeritage! If you already have an account with MyHeritage registered to your email address (******@*****.com), you don't need to do anything -- your account will be automatically credited in 48-72 hours. If you do NOT have an account with MyHeritage (or if your account is registered to an email address other than *****@******.com), please go to www.myheritage.com/family-tree to register an account with this email address. Once registered, your account will be credited in 48-72 hours.
Open a support ticket if it hasn't been credited to your account.
Note: data subscription is NOT free MyHeritage subscription. It's just access to the MyHeritage records.